The bible tells us that we will be judge by the standard of which we judge others. It seems quite fair and simple.
It is fair, but it is not simple. The more we really think of the meaning of the principle the more we see how often we fail.
We constantly tell others not to assume, but we constantly assume ourselves. We criticize others for missing details in their work, but we do not focus on the details in our own work.
It takes many forms, but we are often harder on others than we are on our self. Often the principles of the bible only seem easy because we lack the spiritual discernment to see our lack.
God's grace is overflowing for our lack. He knows our weakness and need for growth. We live day by day by grace even as we grow in the knowledge of our weakness.